U.S. patent number 4,395,775 [Application Number 06/168,700] was granted by the patent office on 1983-07-26 for optical devices utilizing multicapillary arrays.
Invention is credited to Thomas B. Lucatorto, Thomas J. McIlrath, James R. Roberts.
United States Patent |
4,395,775 |
Roberts , et al. |
July 26, 1983 |
Optical devices utilizing multicapillary arrays
Abstract
Optical devices utilizing multicapillary arrays such as beam
splitters, calibrated beam attenuators, collimators, beam steering
devices, beam modulators and phase shifters and lens.
Inventors: |
Roberts; James R. (Boyds,
MD), McIlrath; Thomas J. (College Park, MD), Lucatorto;
Thomas B. (Washington, DC) |
Family
ID: |
22612583 |
Appl.
No.: |
06/168,700 |
Filed: |
July 14, 1980 |
Current U.S.
Class: |
378/145;
250/505.1; 359/634 |
Current CPC
Class: |
G02B
26/02 (20130101); G02B 5/00 (20130101) |
Current International
Class: |
G02B
5/00 (20060101); G02B 26/02 (20060101); A61N
005/10 (); G02B 005/00 (); G02B 027/14 () |
Field of
Search: |
;350/172,96.24 ;313/13CM
;378/149,145 ;250/510,505,213VT |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
P D. Chopra et al., J. Phys. B7, 2421 1974. .
T. B. Lucatorto and T. J. McIlrath, Phys. Rev. Letters, vol. 37,
No. 7, pp. 428-431 (1976). .
T. V. Vorburger et al., Rev. Sci. Instr., vol. 47, pp. 501-504
(1976)..
|
Primary Examiner: Smith; Alfred E.
Assistant Examiner: Grigsby; T. N.
Attorney, Agent or Firm: Ferguson, Jr.; Gerald J. Baker;
Joseph J.
Claims
What is claimed is:
1. An optical device for splitting an incoming beam of radiation
comprising a two-dimensional multicapillary array including a plate
having a plurality of pores extending therethrough parallel to the
incoming beam where said pores comprise an open area of the plate
which transmits a portion of the incoming beam and the remaining
area of said plate surrounding said pores comprises a closed area
which is provided with a planar coating which reflects the
remaining portion of the incoming beam where the normal to said
closed area is disposed at an angle with respect to the incoming
beam.
2. A device as in claim 1 where the power density of said output
radiation is equal to or greater than approximately
300.times.10.sup.6 watts/cm.sup.2.
3. A device as in claim 1 where the wavelength of the radiation is
less than 2000 A.
4. A device as in claim 3 where the wavelength of the radiation is
less than 1050 A.
Description
CROSS REFERENCE TO RELATED APPLICATION
This application is related to an application, Ser. No. 168,698,
entitled "Improved Laser Utilizing Multicapillary Array as Output
Window" filed on even date herewith by the applicants named in the
present application, the foregoing application being incorporated
herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This application is directed to optical devices and to
multicapillary arrays for use therewith.
2. Discussion of the Prior Art
Multicapillary arrays (MCA's) made of perforated stainless steel
plates have been previously reported (see P. D. Chopra et al., J.
Phys. B7, 2421 (1974)) as useful in transmitting radiation at 1216
A although no details of the properties of the arrays were given.
In recent years the technology of producing glass MCA's having
capillaries of very small diameters, tightly packed in arrays
giving large spatial apertures, has been developed in connection
with the development of multichannel plate image intensifiers.
These arrays are now commercially available from Galileo
Electro-Optics Corporation, Sturbridge, Massachusettes. Most of
these arrays have open areas in excess of 50%, are available with
pore sizes between 1.5 .mu.m, and 100 .mu.m, and can be fabricated
in sizes in excess of 10 cm.sup.2. These windows have been used to
separate a vacuum spark (BRV-type) VUV (vacuum ultraviolet) source
and an evacuated, grazing incidence, optical system from a
.about.10.sup.3 .mu. bar vapor cell to obtain atomic absorption
spectra in the 100-400 A spectral region, see T. B. Lucatorto and
T. J. McIlrath, Physics Review Letters, Vol. 37, No. 7, pp. 428-431
(1976). They were also used as an output window on a gas discharge
VUV light source in the 400-1050 A spectral region, see T. V.
Vorburger, et al., Rev. Sci. Instrum., Vol. 47, p. 501 (1976). MCA
applications are also discussed in an article by the present
inventors, see Applied Optics, Vol. 18, page 2505, July 15, 1979.
All of the foregoing articles are incorporated herein by
reference.
OBJECTS OF THE INVENTION
A primary object of the present invention is to provide improved
optical devices utilizing MCA's.
It is a further object of this invention to provide improved
MCA's.
Other objects and advantages of this invention will be apparent
from a reading of the following specification and claims taken with
the drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIGS. 1A and 1B are diagrammatic perspective and side views of an
illustrative beam splitter in accordance with the invention.
FIG. 2 is a diagrammatic perspective view of an illustrative
calibrated beam attenuation in accordance with the invention.
FIG. 3 is a diagrammatic perspective view of an illustrative
collimator in accordance with the invention.
FIG. 4 is a perspective view of an illustrative beam steering
device in accordance with the invention.
FIG. 5 is a perspective side view of an illustrative beam modulator
in accordance with the invention.
FIG. 6 is a diagrammatic cross-sectional view of an illustrative
phase shifter and lens in accordance with the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
Reference should be made to the drawing where like reference
numerals refer to like parts.
Referring to FIGS. 1A and 1B, there is shown a beam splitter 10
comprising an MCA, the faces of which are cut an angle .theta. off
normal to the incoming beam. The angle of the cut is such that a
portion of the VUV radiation goes through and part is reflected
back at the cut angle .theta., thus providing radiation beams in
two different directions.
The MCA has a plurality of pores or capillaries 18 which alternate
with the closed area 20 of the array where the capillaries are
parallel to the incident beam. Coated upon the closed area is a
reflective coating. The MCA together with the coating comprises the
beam splitter where part of the incoming radiation is reflected by
the coating and the remaining part is transmitted through the
pores. By varying the ratio of the open area of the array (that is,
the cross-sectional area of the pores 18) with respect to the
closed area, the ratio of reflected-to-transmitted radiation can be
varied without changing the nature of the reflective coating.
Further, due to the use of the extremely small capillary apertures
18, both the transmitted and reflected beams will sample almost
identical regions (when the open and closed areas are substantially
equal) and thus exhibit identical intensity and coherence
properties. This is essential for two beam X-ray holography or
other interferometric applications such as Mach-Zender or other
interferometers.
The foregoing reflective coating may typically be a multilayer
dielectric coating. Before depositing the coating, the closed area
20 may be optically ground and polished on either one or both of
the surfaces 12 and 14 of the MCA. Layers of Al and MgF.sub.2 are
alternately vacuum deposited to thus form the desired multilayer
dielectric coating. The vacuum deposition of the layers will not
cover over the pores 18. Reference should be made to an article
entitled "Special Application Coatings for the Vacuum Ultraviolet"
by Bruce K. Flint, Paper No. 140-14, given at the SPIE Symposium,
Mar. 29, 1978, which is available from Acton Research Corporation,
Acton, Massachusetts 01720, for a description of VUV, multilayer
dielectric coatings which may be used in the present invention in
the VUV range (approximately 20-2000 A). The provision of such
reflective coatings for longer wavelength ranges is also well
known.
Beam splitter 10 is particularly advantageous in the VUV range as
are the other embodiments of the invention illustrated in FIGS. 2-6
since in this range and, in particular, at wavelengths less than
1050 A, there are only a few metallic thin film coatings which may
be used in certain portions of the range and even these are subject
to contamination, corrosion and even destruction if used in a
moderately intense laser radiation environment. The beam splitter
and other embodiments of the present invention are rugged, have a
broad spectral band pass and provide a large aperture window.
Further, they may be used in the VUV range since the radiation is
transmitted through the pores 18 and not through the material
itself.
Further, the beam splitter and other embodiments of the present
invention illustrated in FIGS. 2-6 are particularly well suited for
use in high power applications regardless of the wavelength
although it is to be understood that these various embodiments may
be used at any wavelength regardless of the power level. Most solid
materials are subject to damage when the power density of the
incident energy thereon is equal to or greater than
300.times.10.sup.6 watts/cm.sup.2. However, again due to the
transmission of the incident energy through the pores 18, the
embodiments of this invention are well suited for transmitting
energy, the power density of which exceeds the foregoing
figure.
Typically, although not necessarily, a vacuum interface is provided
whereby a substantial pressure differential may or may not exist
across the MCA's of FIGS. 2-6. If such a pressure differential is
maintained, the ratio of the diameter of the pores, D, to the
length thereof, L, should be small enough that the flow through the
pores may be characterized as molecular flow. If it is necessary to
retain image or beam quality, the diameter of the pores should be
at least 50.lambda. where .lambda. is the wavelength of the
transmitted radiation and preferably it should be at least
100.lambda., whether or not a substantial pressure differential
exists across the MCA's. If only simple light transmission is
required, the pore diameter should at least be greater than
.lambda.. Further, if it is necessary to maintain coherence between
the reflected and transmitted radiation, the separation, of the
pores should be less than the coherence dimension of the
radiation.
Referring to FIG. 2, there is shown an illustrative calibrated beam
attenuator 22 in accordance with the invention. By measuring the
ratio of the open area 18 to the closed area 20 either optically or
mechanically, a calibrated attenuation of the input radiation may
be effected. For example, the area of a single pore multiplied by
the number of pores (=open area) =A open. The area of incoming
beam=A in. The attenuation factor=A open/A in. Similarly, the
intensity of incoming beam (I in) calibrated by a vacuum photodiode
or the like and the intensity of the outgoing beam (I out)
calibrated similarly produce an attenuation factor=I out/I in. The
use of the extremely small capillary apertures results in the
transmitted beam forming an efficient, homogeneous average of the
total beam. This is in contrast to a system using large apertures
of sampling diaphagms or mirrors. The D/L ratio must be greater
than the solid angle of the radiation.
Referring to FIG. 3, there is shown an illustrative colluminator 24
in accordance with the invention. A preferred use for such a
collimator is the collimation of a large area, uncollimated X-ray
source. The material that comprises closed area 20 is doped with Au
or Pb, for example, to absorb the X-rays. Thus, X-rays not passing
straight through the pores 18 will be absorbed when they impinge on
the walls. Hence, collimated X-rays will issue from the collimator.
The collimator may be used with radiated energy of different
wavelengths. If the wavelength is in the VUV range and, in
particular, is less than 1050 A, it will not be necessary to dope
the material comprising the closed area. A reflective coating may
also be placed on the closed area 20 to prevent passage of rays
other than those passing straight through the pores. The foregoing
considerations also apply to the other embodiments of the invention
where it is desired to transmit energy only through the pores of
the MCA's.
Referring to FIG. 4, there is shown an illustrative beam steering
device 26. Although usable with radiated energy of any wavelength,
the beam steering device 26 is particularly useful with respect to
VUV or X-ray radiation. The MCA is tilted so that a slight angle
.theta. occurs between the incoming radiation and the normal N to
the flat surface 12. This slight tilt angle is such as to allow
radiation to reflect within the pore channels at grazing angles.
This produces an output beam at an angle .phi. with respect to the
incident beam. With curved pore channels, the same effect will
occur and the output beam angle .phi. will depend on the length and
curvature of each pore channel.
Referring to FIG. 5, there is shown an illustrative beam modulator
28 in accordance with the invention which may be used with VUV
radiation, for example, although it can also be used with radiation
of other wavelengths. The beam modulator 28 may be attached to a
vibrating torsion bar scanner 30 or similar device. Due to the low
mass (and thus low inertia) of the MCA comprising beam modulator
28, a VUV beam can be modulated at a high frequency (equal to or
greater than 10 kHz). This provides a factor of about 10 increase
in the frequency of modulation of the beam with respect to prior
art devices for purposes of synchronous detection of VUV radiation,
for example. Thus, the MCA comprising beam modulator 28 may be used
as a chopper of VUV or X-ray radiation at high frequencies because
of the very low mass of the MCA. If it is necessary to collimate
the input radiation to beam modulator 28, a collimator 24 of the
general type illustrated in FIG. 3 may be employed.
Referring to FIG. 6, there is shown an illustrative phase shifter
and lens 32 in accordance with the invention. The length of the
pores 18 are different due to the convex curvature 34 of the output
side of element 32. Since transmission through a pore 18 results in
a phase shift which depends on the length of the pore, the element
32 will cause a wavefront distortion resulting in focusing or
de-focusing of the input beam. Use of an array of equal length
pores produces a phase shifter. This has applications to
interferometers and other phase sensitive instruments. The surface
34 may be concave whereby the output radiation would diverge.
As indicated hereinbefore, the various embodiments of this
invention are particularly suitable for use as high power elements.
This is also because a reflective coating may be provided on the
closed area 20, as discussed hereinbefore with respect to FIG. 1,
to lessen damage of the closed area while the high power radiation
is transmitted through the pores 18 without damaging the device,
the foregoing being particularly applicable to the embodiment of
FIG. 6.
It is to be understood that the above detailed description of the
various embodiments of the invention is provided by way of example
only. Various details of design and construction may be modified
without departing from the true spirit and scope of the invention
as set forth in the appended claims.
* * * * *